For anyone wondering about the dislikes number in YouTube, Google decided to remove them in order to "help creators" and stop imaginary "hate". This extension allows you to restore that functionality in YouTube to the old standard.
https://addons.mozilla.org/en-US/firefo ... -dislikes/
Also I improved a bit the steps to make it work after the add-on is installed since Google's UI is terrible and took me a time to get to the last step.
1. Sign into google account
2. Go to https://console.cloud.google.com/apis
3. Create a new Project
4. Create new API key credential for project (Credentials --> Create Credentials)
5. Copy and paste API key to "YouTube Restore Dislikes" add-on options and click save
6. Go to https://console.cloud.google.com/apis and click on "ENABLE APIS AND SERVICES" (Dashboard --> Enable APIs and Services)
7. Search "YouTube Data API v3"
8. Click Enable
P.D. Today Dec. 13th, Google has disabled the API that allowed the add-on to obtain the number of dislikes data